Two studies related to yeast wall structure examined (1) the role of mannoproteins in cell wall premeability and (2) the function of cell division cycle (cdc) gene 3 in septum formation. These studies were performed in collaboration with the laboratory of E. Cabid, NIADDKD. The first study showed that mannoproteins which coat the outer surface of the yeast cell wall function in part to control cell wall porosity and hence some to protect the plasma membrane from external lytic agents. In the second study we examined yeast with a temperature sensitive mutation of cdc gene 3, which results in failure of cytokinesis. At the non-permissive temperature the mutant cells form septa which are similar in structure and chemical composition to normal septa. However, the septa fail to form at the junction of the bud and mother cell, but rather cut off peripheral bits of cytoplasm at their aberrant locations. Results with double mutants showed that septum formation requires prior events of DNA synthesis and nuclear division, and that the cdc 3 gene product is required for correct location but not the formation of the septum.